Degree of oligotrophic status makes a difference on the microbial community structure at deep sedimentary biosphere of South Pacific Gyre

Abstract

The IODP (Integrated Ocean Drilling Program) Expedition 329 had been progressed from 9 October to 2 December 2010 to study the subseafloor life of the SPG (South Pacific Gyre). SPG is the largest ultra-oligotrophic environment on the earth and chlorophyll concentration of surface is very low, so the amount of organic compounds by primary production supplied to abyssal sediment is low. During the exploration period, 7 sites (U1365~1371) were drilled. Of these, 6 sites (U1365~1370) tended to penetrate oxygen more than 50mbsf. However, U1371 showed a significant difference that TOC concentration is relatively higher than other sites in overall depth and oxygen penetration is detected only within 1mbsf. Therefore, we wanted to know the microbial community structure forming the deep biosphere each site by selecting several depths exhibiting distinct features at each 3 sites (U1365, U1370, U1371). For this purpose, 16S rRNA sequence amplicon analysis was performed to compare the microbial community pattern difference between the three core sites. As a result, Chloroflexi (Dehalococcoida) was highly dominant at majority of depths in the three sites. The distinctive feature of U1371 is figured out that the bacteria such as SAR406, SAR202 and Desulfobacterales which are able to use nitrate, sulfate instead of oxygen can be detected correspondingly to characteristics of each depths.h and chlorophyll concentration of surface is very low, so the amount of organic compounds by primary production supplied to abyssal sediment is low. During the exploration period, 7 sites (U1365~1371) were drilled. Of these, 6 sites (U1365~1370) tended to penetrate oxygen more than 50mbsf. However, U1371 showed a significant difference that TOC concentration is relatively higher than other sites in overall depth and oxygen penetration is detected only within 1mbsf. Therefore, we wanted to know the microbial community structure forming the deep biosphere each site by selecting several depths exhibiting distinct features at each 3 sites (U1365, U1370, U1371). For this purpose, 16S rRNA sequence amplicon analysis was performed to compare the microbial community pattern difference between the three core sites. As a result, Chloroflexi (Dehalococcoida) was highly dominant at majority of depths in the three sites. The distinctive feature of U1371 is figured out that the bacteria such as SAR406, SAR202 and Desulfobacterales which are able to use nitrate, sulfate instead of oxygen can be detected correspondingly to characteristics of each depths.